


Questions of Compatibility

by sindontquit



Category: Undertale (Video Game)
Genre: BDSM, Bad Sex, Dubious Consent, Fellcest - Freeform, M/M, Rape Fantasy, Underfell, honeymustard - Freeform
Language: English
Status: In-Progress
Published: 2017-06-17
Updated: 2017-06-17
Packaged: 2018-11-15 09:31:08
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,427
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11228184
Author URL: https://archiveofourown.org/users/sindontquit/pseuds/sindontquit
Summary: Sans loves Stretch. He does. But as their relationship approaches the 4-year mark, he begins to have questions. "Why is the sex so bad these days?" is near the top of the list. The answers he comes up with raise more questions-- of respect, worth, effort, compromise, and compatibility.Is there, perhaps... someone else who might fit what Sans needs?(Slowly deteriorating Honeymustard that eventually turns into Fellcest.)





	Questions of Compatibility

**Author's Note:**

> This is my first longer work. It's plot heavy, but there will be plenty of smut. Probably in every chapter, because that's just the kind of person I am.

Stretch slid his fingers around the back of Sans' neck, gripping gently. The other hand grasped Sans' chin more firmly, tipping it up to meet Stretch's kiss. Sans kissed him back, wanting so badly to be enjoying it.

He'd been wanting that for a long while. Their relationship, a couple of years old already, was starting to feel to Sans like a well-loved jacket he'd grown slightly too big for. The wish was there. The comfort was there. But the sleeves of an old jacket are missing a few crucial inches of fabric, which you can try to grasp for, but which will never be there again. 

In Sans' thoughts, at least. Stretch didn't seem to share the opinion. In fact, he'd grown more affectionate in proportion to Sans' lack of enthusiasm. Despite his best efforts, Sans had never been great at hiding his feelings. 

All of this passed through Sans' mind as Stretch deepened the kiss. His magic responded, sort of-- a red glow grew slowly along his pelvis where he sat on Stretch's bed. Stretch, orange magic looking eager, pressed Sans backward to lay down, licking at his cervical vertebrae. His hands trapped the smaller's, pinning them above his head. 

"Are you my dirty little slut, huh?" Stretch murmured in Sans' ear.  
It was a familiar question. One Sans was highly accustomed to saying "yes, Sir" to.  
"Yes... Sir." he muttered in reply.

Stretch gave a pleased hum and began to move against him, tracing along Sans' spine and iliac crests only for a few moments before reaching for his pubis impatiently. 

Sans wished he wouldn't go straight for it like that. It was too sensitive, Stretch's long phalanges stimulating him so quickly it felt more irritating than arousing. 

But Sans didn't stop him. He couldn't really think of a way to stop him, without breaking up with him then and there, because he knew Stretch. As laid back as he pretended to be, there was a deep and desperate loneliness in him, and a single small rejection on Sans' part would turn a relatively pleasant evening into an angsty interrogation. 

"Hips up, slut." Stretch tugged Sans' shorts down his femurs, throwing them to the floor. Sans resigned himself. Maybe there was a way he could enjoy this, if he framed it right in his head.

As Stretch's orange tongue licked along his pelvis, Sans shut his eyes in the darkness of the bedroom and accessed some of his darker kinks. He amplified how much he didn't want this. This was an assault. A forced encounter by... hmmm... a strange monster. Something kind of gross... a dog monster, maybe? Who'd forced his way into Sans' bedroom... and if he didn't call him "Sir," the monster would dust him. Sans was going to have to endure it to save his own life, even as the dog monster used his body for its pleasure.

Red magic finally bloomed into a pussy, and he moaned, bucking up into Stretch's tongue. Sans could practically feel the taller skeleton's relief that he was finally showing some enthusiasm.

The golden tongue pressed roughly against his clit and then immediately went for his entrance, squirming inside and slicking it up with orange magic. Stretch had his cock out and was stroking it, breathing harshly against Sans' pussy. 

(The dog monster was panting, tongue lolling out, drooling disgustingly onto him.)  
"Aaahh... fuck... mmn..." Sans whimpered. "Please..."  
("Please, don't do this!" He begged, even as thrills of pleasure ran down his spine from the feeling of the monster's tongue. He shouldn't be enjoying it. He was disgusting for enjoying it. But the monster was forcing him to...)

Stretch climbed up over him, grinding their magic together. "Please, huh?" he panted. "You want my cock that badly, little whore?"  
"Y-yes, Sir..."  
("No! Don't--")

Stretch shoved his femurs apart and thrust inside, rolling his hips to try to get deeper. Sans' magic, however, was offering some resistance. Not surprising, considering Stretch hadn't actually been trying to make him come with his tongue. Just... wet enough to stick his cock into. 

Sans swallowed his bitterness and incorporated it into his fantasy. (Of course it hurt, of course the dog monster was forcing his way in, this was a rape, after all.)

His magic began to lubricate then (the thought that he was sick for getting turned on by that fantasy only turned him on further) and he wrapped his legs around the taller skeleton's hips. Stretch hilted himself with a pleasured grunt. 

"Oh, ffffffuck..." Sans rolled his hips up as Stretch began to move, pressing him down into the mattress under his weight. Writhing under his lover, Sans strained against the phalanges that were once again grasping his wrists.

(He struggled, fruitlessly, against the heavy dog monster as it impaled him with its cock.)

He wanted Stretch to be rougher so the fantasy would work better. To that end, Sans filled his expression with sexy defiance and began to buck in earnest. "Come on, Stretch," he panted. "Is that the best you got?"  
Stretch growled down at him. "Is that the best I've got? Oh, you're in for it now, fucktoy." The taller skeleton kept his wrists pinned in one hand, reaching into his rib cage with the other and grasping his soul. Stretch squeezed, the magical equivalent of a chokehold. Sans gasped in pain and pleasure, squeezing his sockets shut.

(He'd failed to call the dog monster "Sir," and now he was going to pay for it.)

He rolled his hips more urgently into his lover's thrusts. Stretch squeezed his soul harder, pounding into him, and Sans made pathetic gasping sounds that would have been howls if he could breathe. The mattress creaked wildly under their increasingly desperate motion.

Sans' physical ecstasy was overpowering his thoughts. Everything was growing blurry and hot and confused, and the face of the person fucking him was flashing between Stretch's skeletal grin and a dog monster's toothy red glare. He wanted more. He twisted his body side to side in a purely theatrical attempt to throw the other off, staring up into 

Glowing orange eyes.  
(Glowing red eyes.)

Stretch released his soul, withdrew his hand, and raised it. Sans' soul seized in delighted anticipation.  
Stretch backhanded him across the face. 

"Fuck!" Sans' skull rocked to the side and he arched sharply, pleasure flooding his body. As his skull rebounded, Sans' mind smashed his fantasy against his reality. His sockets widened in confusion for a heartbeat before he came suddenly with a trembling gasp, yanking one hand free to clamp over his mouth as he squeezed his sockets shut. 

Above him, Stretch moaned freely, his now unoccupied hands grasping Sans' pelvis and pulling it up to meet his desperate thrusts.  
"FUCK, Sans... MMMH!"  
Stretch came, his orange cock buried as deep in the smaller's magic as it would go, throbbing against the still-pulsing red walls. Sans moaned beneath him, the sound still muffled in his hand, lost in aftershocks.  
The two skeletons lay still for several long moments, their magic still entangled, before Stretch finally pulled out. He collapsed next to Sans with a contented sigh.

As he returned to reality, Sans curled into Stretch's side. "Mm, thank you, babe," he murmured. He mostly meant it. It had been a pretty good orgasm. The taller skeleton seemed to find it sincere, gathering his small lover into his arms and nuzzling the top of his skull.  
"Was the slap okay?" He murmured. "It... really seemed like you wanted it."  
"Yeah, I did," Sans sighed sleepily. "It was hot."  
Stretch stroked the place he'd hit gently before sitting up to pull the blankets over them both. 

\--------------------------------------------------------------------------------------------------------------------------

"GOD DAMMIT!"  
Sans, halfway through his front door, ducked instinctively. This time, however, his brother's anger didn't seem directed at him. Pots clanged from the kitchen and Sans crept slowly closer as the smell of badly burnt pasta reached him. 

His brother was facing away from the door, presumably glaring furiously down at the pan Sans could just see in front of him. Sans leaned into the doorway.  
"...Paps?"  
"WHAT?!"  
Papyrus spun around, eyelights blazing, and stared murderously at his smaller brother. As Sans looked up at the flaming red of Papyrus' eyes, his soul shivered in bewildering recognition. He took a shocked step backward.

"Uh... NothingI'mgoingupstairslaterbro!"

Sans teleported directly into his room and shut the door, breathing harshly. The lights were still off, but the red glow he was casting all over the carpet around him was beyond obvious. 

What the fuck just happened? Sans wondered.


End file.
